I haven't done formal volunteer aid, but did some medical clinics in Kenya as part of a mission trip there in 1998. It was extremely rewarding because people there had no access to physios, and little access to basic medical care. I was able to teach mums chest physio for their babies and children with chronic lung problems, teach pregnant womens groups about post natal exercise and back care, as well as help many individuals with pain. I also did a lot of first aid type stuff (including steristripping a 3 week old machete wound on a shin) as well.There were heaps of crippled kids (from polio) and amputees hopping holding sticks or driving home made wheelchairs on the streets, who I would have loved to be able to help but would have needed to stay a few months to be effective in helping them. It was probably more beneficial for me than the people though- it will change you to see how some people live and still keep smiling!!